Linking Up Cleanly

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Science  23 Nov 2007:
Vol. 318, Issue 5854, pp. 1219
DOI: 10.1126/science.318.5854.1219c

Selective coupling of aryl molecules is a crucial step in the preparation of a wide range of commercial organic compounds. The requisite selectivity has traditionally been achieved by appending mutually reactive groups (such as halides and boron- or tin-based substituents) to each partner, but the addition and elimination of such groups generate considerable waste material. Recent advances in transition metal catalysis have offered a promising alternative approach, in which C-H bonds on the aryl rings are oxidatively cleaved directly to yield a C-C bonded biaryl product and (ideally) water as the sole byproduct. Li et al. extend this method to the coupling of acetylated anilines with alkyl benzenes. The acetamide group directs a palladium catalyst to react selectively with an adjacent ortho C-H bond, and a second C-H scission links up the benzene partner. In the case of NH(acetyl) substrates, a subsequent sequence involving N-H and C-H scission leads efficiently to carbazole products with a fused central C4N ring connecting the aromatic cycles on either side. The reactions proceed under oxygen at 120°C, with varying amounts of a cupric salt added as a co-catalyst depending on the substrates. — JSY

Angew. Chem. Int. Ed. 46, 10.1002/anie.200704092 (2007).

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